The present invention relates to coal-burning furnaces and especially to those, termed boilers, adapted for heating water or similar fluids flowing therethrough.
With the rapidly rising cost of fuel oil, natural gas and electricity, attention is increasingly being directed to the use of coal and wood for home heating. Unfortunately, there is a general lack of understanding that wood and coal differ significantly and that the efficient use of coal requires a furnace properly designed therefor.
The burning of coal, unlike the burning of wood, is necessarily a two-step process involving primary combustion of the coal, during which combustible gases are produced, and secondary combustion or combustion of the gaseous products of the primary combustion. Air involved in the primary combustion is known as primary air, while air involved in the secondary combustion is known as secondary air.
It is known, in the prior art, to provide for the combustion of these combustible gases, generally through the addition of controlled amounts of secondary air. Existing furnaces, however, are often designed to accept both coal and wood, which yield vastly different amounts of combustible gas, and, therefore, are not optimally efficient in the use of either fuel. Further, such furnaces are generally intended to maximize heat transfer to the surrounding room air, by conduction and radiation, rather than to a working fluid, such as water, passing through the furnace. Thus, these furnaces are not adapted for use in a central heating system, especially such a system integrated with a domestic hot water system.
Finally, existing furnaces are seen to suffer in that they generally include a firebox comprising a single casting or welded assemblage, of tremendous weight, which renders transportation and installation of the furnace difficult and costly.
It is, therefore, a primary object of the present invention to provide a coal-burning furnace having increased efficiency. This is accomplished, in general, by a furnace wherein gases, generated by the primary combustion of the coal, are collected beneath a transverse baffle member and there burned, the hot burned gases then being passed around the baffle before exiting the furnace. More specifically, primary air is admitted through the front of the furnace, below the grate, while secondary air is admitted through the rear of the furnace, immediately below the baffle member.
It is another object to provide a coal-burning boiler adapted for use in an integrated central heating and domestic hot water system. This is accomplished, in general, by the provision of a heat transfer member adapted for the efficient heating of water passed therethrough. More specifically, the previously mentioned baffle member may advantageously comprise a pair of parallel plates and a plurality of parallel channel wall members extending perpendicularly therebetween, the channel wall members being alternately longitudinally offset, each contacting but one of a pair of end walls, so as to form a continuous fluid flow channel for passage of a stream of water through the boiler.
It is yet another object to provide a coal-burning furnace which may be readily transported to the installation site and there installed without the need for heavy lifting equipment. This is accomplished by a furnace comprising relatively readily transportable upper and lower firebox halves having mating, outwardly turned, flanges. The flanges, which provide the necessary firebox rigidity, are bolted together, in facing relation, to assemble the furnace at the place of installation.
It is still another object to provide a furnace of the aforementioned character and kind which is simple and economical of fabrication.